(a) Field of the Invention
The present invention relates to a timing chain system, and in particular, to an improved sprocket assembly for an automotive timing chain system capable of reducing noise.
(b) Description of the Related Art
As well known, internal combustion engines employ poppet valves that are operated by a camshaft that is driven by a crankshaft, with a suitable timing mechanism, and timing chains are used to transmit power and motion between the camshaft and the crankshaft. These chains are formed of ranks of links interleaved with adjacent ranks of links and having aligned apertures for receiving pivot pins to join the ranks and provide articulation of the chain as it passes around the driving and driven sprockets.
FIG. 1 shows a conventional internal combustion engine embodying a timing chain and sprocket system.
As shown in FIG. 1, a driving sprocket 51 on the crankshaft 60 and the driven sprocket 52 on the camshaft 61 are connected to each other by a timing chain 53. The sprockets 51 and 52 have a plurality of teeth 62 equally spaced around the circumference of the driving and driven sprockets 51 and 52, and the timing chain 53 consists of pairs of inside links 54 alternating with pairs of flanking guide links 65 joined by pivot pins 55 insulated by rollers 56 such that the chain 53 engages the driving and driven sprockets 51 and 52.
The tension of the timing chain 53 is adjusted by a damper 58 and a tension device 59 mounted to an engine block.
In this configuration, the engine torque is transmitted to the drive sprocket 52 via the crankshaft 60 and consequently to the driven sprocket 52 on the camshaft 61 by the chain 53 such that the camshaft 61 rotates so as to operate a valve system.
FIG. 2 is an enlarged view of a camshaft sprocket engaged with the chain. As shown in FIG. 2, the chain 53 wraps on the sprocket 52 in a way that the pivot pins 55 having rollers 56 are inserted between the teeth 62 such that the teeth on the sprocket act to transfer a load from the chain 53.
In this timing chain system, however, the friction surface between the rollers 56 insulating the pivot pins 55 and the driven sprocket 52 is large so backlash is generated, and in particular there exists a gap xe2x80x9cCxe2x80x9d between the pivot pin 55 and the roller 56 such that vibration noise is caused by engine resonance. Also, the rollers 56 generate noise when they contact the sprocket 52.
The present invention has been made in an effort to solve the above problems of the prior art.
It is an object of the present invention to provide an improved sprocket for a timing chain system allowing a reduction in backlash between the chain and the sprocket by integrally forming an auxiliary sprocket with the driving and driven sprockets, resulting in a reduction of noise.
It is another object of the present invention to provide an improved sprocket for a timing chain system capable of preventing vibration noise from between the pivot pin and the roller from being generated by integrally forming an auxiliary sprocket with the driving and driven sprockets.
To achieve the above object, a sprocket assembly for an automotive timing chain system comprises a main sprocket, an auxiliary sprocket mounted onto one side of the main sprocket for assisting the main sprocket, and an elastic member elastically coupling the auxiliary sprocket to the main sprocket for generating an elastic force between the main and auxiliary sprockets.